The Supreme Court ruled on Monday that police cannot put a GPS device on a suspect's car to track his movements without a warrant.

The high court ruling was a defeat for the Obama administration, which had argued that a warrant was not required to use global positioning system devices to monitor a vehicle on public streets.

The justices unanimously upheld a precedent-setting ruling by a U.S. appeals court that the police must first obtain a warrant to use a GPS device for an extended period of time to covertly follow a suspect.

The high court ruled that placement of a device on a vehicle and using it to monitor the vehicle's movements was covered by U.S. constitutional protections against unreasonable searches and seizures of evidence.

The case began in 2005 when Antoine Jones, owner and operator of a nightclub in the District of Columbia, came under suspicion of trafficking in narcotics and was made the target of an investigation by a joint FBI and Metropolitan Police Department task force.

Officers employed various investigative techniques, including visual surveillance of the nightclub, installation of a camera focused on the front door of the club, and a pen register and wiretap covering Jones?s cellular phone. Based in part on information gathered from these sources, in 2005 the Government applied to the United States District Court for the District of Columbia for a warrant authorizing the use of an electronic tracking device on the Jeep Grand Cherokee registered to Jones's wife. A warrant issued, authorizing installation of the device in the District of Columbia and within 10 days.

On the 11th day, and not in the District of Columbia but in Maryland, agents installed a GPS tracking device on the undercarriage of the Jeep while it was parked in a public parking lot. Over the next 28 days, the Government used the device to track the vehicle's movements. By means of signals from multiple satellites, the device established the vehicle's location within 50 to 100 feet, and communicated that location by cellular phone to a Government computer. It relayed more than 2,000 pages of data over the 4-week period.

The Government ultimately obtained evidence, which played a key role in his conviction for conspiring to distribute cocaine.

The appeals court had thrown out Jones's conviction and his life-in-prison sentence, and ruled prolonged electronic monitoring of the vehicle amounted to a search.

The justices agreed in upholding the appeals court decision, but at least four justices would have gone even further in finding fault not only with the attachment of the device, but also with the lengthy monitoring.

Justice Antonin Scalia said attachment of the device by the police was a trespass and an improper intrusion of the kind that would have been considered a search when the Constitution was adopted some 220 years ago.